1. Field of the Invention
This invention related to adjusting the throttle plate on an electronically controlled engine.
2. Prior Art
An idle speed control system can include controlling airflow through a throttle and a throttle bypass airflow path. Typically, the duty cycle of an air bypass valve solenoid in the bypass air path is regulated to obtain the desired engine speed based on predicted airflow. The airflow is adaptively corrected to minimize the impact of hardware variability.
The predicted mass airflow is determined as a function of the desired engine idle speed maintained by the idle speed control system. The desired idle airflow has two components: throttle plate leakage and bypass valve airflow. An engine control strategy calculates the total desired idle airflow. The required airflow through the air bypass valve is then obtained by subtracting the throttle plate leakage term from the total idle airflow. The duty cycle output to the air bypass valve solenoid, which determines the air bypass valve position, is determined from a transfer function based on known characteristics of the air bypass valve.
Due to hardware variability, the predicted mass airflow is adjusted by an integration term, based on rpm error, and an adaptive term which was previously learned and stored in a memory of the on-board computer.
Various methods for adjusting a throttle plate to achieve a desired engine speed with zero integration error at idle are known. For example, relatively complex idle speed setting procedures include the following steps:
1. Unplug spark control line and verify that ignition timing is Base .+-.2 degrees before top dead center. PA1 2. Remove positive crankcase ventilation (PCV) hose from throttle body and plug it. Remove canister purge hose from throttle body and connect it to the positive crankcase ventilation connector of the throttle body. PA1 3. Remove positive crankcase ventilation hose at the positive crankcase ventilation valve and install .200 inch diameter orifice. PA1 4. Disconnect idle speed control-air bypass solenoid. PA1 5. Start engine and run at a predetermined rpm. PA1 6. Place automatic transmission in park or drive; manual transmission in neutral. PA1 7. Engine off, back out throttle plate stop screw clear off the throttle lever pad. PA1 8. With a .010 inch feeler gauge between the throttle plate stop screw and the throttle lever pad, turn the screw in until contact is made then turn it an additional predetermined number of turns. PA1 9. Check/adjust idle rpm: turn the throttle plate stop screw to a predetermined (rpm); shut engine off, and repeat Steps 5, 6, 9. PA1 10. Shut engine off and disconnect battery for 3 minutes minimum. PA1 11. Engine off, reconnect spark control line. PA1 12 Remove canister purge hose from positive crankcase ventilation connector of throttle body and reconnect it to its canister purge fitting. Unplug positive crankcase ventilation hose and reconnect it to its positive crankcase ventilation fitting. PA1 13. Remove orifice from positive crankcase ventilation hose and reconnect to positive crankcase ventilation valve. PA1 14. Engine off; reconnect idle speed control-air bypass solenoid; verify the throttle is not stuck in the bore and linkage not preventing throttle from closing. PA1 15. Start engine and stabilize for 2 minutes; then increase engine speed and let it return to idle; lightly depress and release the accelerator let engine idle. PA1 (1) Variability factor eliminated--Physical adjustment of the throttle plate optimizes idle speed control function of the bypass air valve thus adaptive corrections minimized. PA1 (2) Previously learned adaptive memory is cleared during test procedure to establish zero baseline. PA1 (3) Process is common to all engine families--Individual specifications, once unique, become transparent as they are built into the calibration. PA1 (4) Improved serviceability/accuracy--Procedure is contained in the vehicles on-board computer and requires engine controls validation prior to service mode. Eliminates tampering/defaulting control system, special tools, and equipment error (tachometer). PA1 (5) Fuel and spark control systems are used as a means to optimize the desired idle speed. There is no need to disable these systems or the idle speed control system. PA1 (6) Automates current idle adjustment procedures --Eliminates matrix method of individual procedures. PA1 (7) Predictable/repeatable/reliable--Interactive with idle speed control strategy and engine calibration. System-to-system variables are not perceived by the customer and field service.
Yet other ways of controlling idle speed are known.
U.S. Pat. No. 4,601,199 issued to Denz teaches a diagnostic system for determining whether an idle bypass valve is functioning properly at various engine speeds.
U.S. Pat. No. 4,483,186 issued to Parel teaches a process for adjusting a throttle plate to achieve a flow rate comparable to that attained when the carburetor was new. That is, for determining the amount of wear of the movable parts of a carburetor, the throttle of the carburetor is retained in a position where it defines a predetermined cross-sectional flow area with the hole of the induction passage. That predetermined area is the area for which, when the carburetor was new, the edge of the throttle was midway along the bypass aperture of the idling circuit. The degree of vacuum in the idling circuit of the carburetor is then compared with a reference value which is the degree of vacuum which prevails on the carburetor in brand new condition under the same operating conditions.
U.S. Pat. No. 4,750,352 issued to Kolhoff discloses a system for measuring airflow at idle taking into account flow through the throttle bore at closed throttle and flow through an idle air bypass valve. A throttle bore has a throttle for varying the effective area of the throttle bore and throttle bypass passage including a bypass valve for varying the effective area of the bypass passage. The air meter determines the airflow into the engine based upon the effective area established by the throttle and the bypass valve and where at closed throttle position the effective area of the throttle at closed position is determined based upon the airflow into the engine through the bypass passage when the engine idle speed is controlled to a predetermined idle speed.
It would be desirable to have a simplified and more predictable way of setting the idle speed control. The method should take much less time and be simple to use without much training. These are some of the problems this invention overcomes.